Vibration induced fatigue failure is a major cause of pipework failure, in particular welded connections between small bore connections (SBCs), typically 0.5″ to 2″ diameter, and Main Liness, typically >2″.
The likelihood of failure increases if the main line pipe experiences operational vibration or transient vibration events or if the frequency of vibration of the SBC matches any of the operational frequencies. The likelihood of failure is highest in the case of large unsupported valves on small diameter SBCs which are excessively long.
The most common retro-fit solution to such problems is to fit substantial bracing in accordance with the good practice methods detailed in the Energy Institute Guidelines. This requires the SBC to be braced back to the parent pipe with supports which have suitably high stiffness to provide effective support against movement in all 3 planes. In many cases, operators fit braces which are ineffective and so not satisfy the EI Guidelines.
One of the main problems in accurately designing a retrofit brace of sufficient stiffness is in obtaining sufficiently accurate dimensions for often complex compound pipe geometries to enable the brace to be designed and fabricated offsite. Consequently, it is common for such braces to be of poor fit which can result in incorrect and ineffective installation or else can impart high static stresses in the SBC in forcing it to fit the brace.